Microneedles (micropiles, micromissile capsules) are under study as a pharmaceutical technology to transdermally administer drugs with high efficiency, where drugs have very low bioavailability and/or low pharmacological availability by a conventional transdermal administration such as painting onto the skin. Microneedles are fine needles that do not give pain even when inserted into the skin. As the materials for microneedles, in addition to the metals used as the conventional injection needles, microneedles made of materials such as silicon have been developed (Non-Patent Documents 1 and 2). These microneedles have the same hollow structure as injection needles, and are used for the injection of drug solution.
Furthermore, self-dissolving type microneedles having biosoluble substance as a base are also developed. Where the target substance is held in the base and is administered into the epiderm followed by the self-dissolution of the base when it is inserted into the skin. For example, Patent Documents from 1 to 3 disclose self-dissolving type microneedles made of maltose as a base. Furthermore, Non-Patent Document 1 discloses self-dissolving type microneedles in which a base is made of polycaprolactone, polylactic acid, or polyglycolic acid. Patent Document 4 discloses a device or an instrument for injecting a drug via microneedles.
Patent Document 5 discloses microneedles in which a base is made of water-soluble and biosoluble thread-forming polymer. The microneedles increase skin permeability of peptides/proteins such as insulin, erythropoietin and interferon, polysaccharides such as heparin, and vitamin C that are poorly-absorbable through the skin.
Patent Document 6 discloses microneedles in which insoluble particles are localized at an acral side of a microneedle. However, because the acral side becomes brittle with this configuration, it is difficult to maintain physical strength, and there is a possibility to make problems when microneedles are inserted into the skin.
Examples in which microneedles are applied on the body surfaces other than the skin are known. For example, in Non-Patent Document 3, an example in which microneedles are applied onto the cornea is disclosed.    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-238347    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2005-154321    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2005-152180    [Patent Document 4] WO 2004/000389 Pamphlet    [Patent Document 5] WO 2006/080508 Pamphlet    [Patent Document 6] WO 2007/030477 Pamphlet    [Non-Patent Document 1] D. K. Armini and C. Lui, “Microfabrication technology for polycaprolactone, a biodegradable polymer”, Journal of Micromechanics and Microengineering, 2000, Vol. 10, pp. 80 to 84    [Non-Patent Document 2] M. R. Prausnitz, Microneedles for transdermal drug delivery, Advanced Drug Delivery Reviews, 2004, Vol. 56, pp. 581 to 587    [Non-Patent Document 3] J. Jiang, Coated Microneedles for Drug Delivery to the Eye, Investigative Opthalmology & Visual Science, 2007, Vol. 48, pp. 4038 to 4043